Rapid and effective repair of bone defects resulting from injury, disease, infection, surgery, aging, tumor, or other pathologic conditions has long been a goal of orthopedic surgery. Over the years, a plethora of compositions and materials have been developed, used and/or proposed for use in the repair of bone defects. The biological, physical, and mechanical properties of these compositions and materials are major factors that influence their suitability and performance in various orthopedic applications.
Millions of bone graft procedures are performed each year worldwide, about half a million of which are performed in the United States alone. Of the latter, approximately a quarter million procedures involve the spine. The bone graft and bone substitute products employed in these procedures may include, for example, bone substitutes, bone dowels, bone matrix (BM) products, tissue engineered matrices, and other allograft precursor bone materials.
Mammalian bone tissue is known to contain one or more proteinaceous materials, presumably active during growth and natural bone healing, that can induce a developmental cascade of cellular events resulting in endochondral and intramembranous bone formation. The active factors have been exchangeably referred to in the literature by various terms including bone morphogenetic or morphogenic proteins (BMP), bone inductive proteins, bone growth or growth factors, osteogenic proteins, osteoinductive proteins, or osteoinductive factors. It has been reported that these growth factors modulate the differentiation of progenitor cells into osteoprogenitor cells, which are responsible for bone and cartilage formation. For example, osteoinductive factors are present within the compound structure of bone tissue, including cortical bone tissue, at very low concentrations, e.g., 0.003% usually reported in ng (nanogram) and pg (pictogram) quantities, and direct the differentiation of pluripotential mesenchymal cells into osteoprogenitor cells that form osteoblasts. Proper demineralization of cortical bone exposes the osteoinductive factors, rendering the bone osteoinductive.
Another aspect of this invention for bone formation and tissue regeneration relates to physiologic mimicry of biologic scaffolds, microenvironments, proteins, growth factors, precursor minerals that prompt osteogenesis. Cells form bone and seek microenvirons in the implanted vicinity to attach, proliferate and differentiate into bone forming precursors and cells. The healing cascade is governed by the similarity and presence of these bioavailable structures and components. The success of a bone graft is determined by its ability to recruit host cells to the site of the graft and modulate their conversion into bone forming cells such as osteoblasts, to repair the defect. This will depend on the osteoconductive, osteoinductive and osteogenic capabilities of the graft. Currently, autograft bone harvested from the iliac crest is considered the “gold standard” due to its superior osteogenic properties. In addition, an autologous bone graft avoids histocompatibility and infectious disease issues. However, autologous bone is limited in supply, is generally painful to the patient upon harvesting, and may lead to significant donor site morbidity (i.e., it may require additional surgical incisions in the patient, may lead to surgical complications, blood loss and may cause additional patient discomfort, and may ultimately increase patient recovery time). Thus, allograft bone is a logical alternative to autograft bone. However, the allograft bone must be rigorously processed and terminally sterilized prior to implantation to remove the risk of disease transmission or an immunological response. This processing can potentially remove the osteogenic and osteoinductive properties of the graft, leaving only an osteoconductive scaffold. These scaffolds are available in a range of preparations (such as morselized particles and struts) for different orthopaedic applications. Some disadvantages of allograft bone grafts include issues relating to histocompatibility, such as rejection by the recipient's immune system, the potential harboring of infectious agents, and diminished physical characteristics such as poor malleability or mechanical properties (e.g., elasticity, compressibility, resiliency, and the like) due to high calcium and mineral content, much of which is discarded during conventional processing.
Presently available bone graft substitutes developed in the art usually have many of the same disadvantages as outlined above with regard to allograft bone grafts. Bone allograft or synthetic graft substitute products are generally formulated as putty and gel type fillers, designed to be inserted into surgically created or congenital bone defects (i.e., defect or void fillers). Traditionally, bone graft substitutes may be made from allogeneic bone chips, granules, or bone powder, or synthetic materials with or without carrier compositions. Additionally, there are a few xenogeneic bone graft products available that are made from bovine bone. Disadvantages of the xenogeneic bone graft products are similar to those observed with allografts, including potential immune reaction to xenogeneic bone and infectious agents, including prions.
Demineralized Bone Matrices (DBM) is one example of allograft bone that has had the inorganic minerals removed, leaving behind the organic “collagen” matrix. The removal of the bone minerals exposes more biologically active bone morphogenetic proteins and increases the osteoinductivity of the graft, resulting in DBM that has superior biological properties and activity spectrum than undemineralized bone grafts. Conversely the mechanical properties of the DBM are significantly altered and/or diminished.
It has been reported that DBM that is derived from cortical bone is an osteoinductive material, because it induces bone growth when implanted in an ectopic site of a rodent, owing to the osteoinductive factors contained within the DBM. It has also been reported that such DBM contains numerous osteoinductive factors, e.g., BMP 1-15, which are part of the transforming growth factor-beta (TGF-beta) superfamily. Of this family, BMP-2 has become the most important and widely studied of the BMP family of proteins. There are also other proteins present in DBM that are not osteoinductive alone but still contribute to bone growth, including fibroblast growth factor-2 (FGF-2), insulin-like growth factor-I and -II (IGF-I and IGF-II), platelet derived growth factor (PDGF), VEGF (Vascularized Endothelial Growth Factor) promoting angiogenesis, and transforming growth factor-beta 1 (TGF-beta.1).
Currently, there is a range of DBM products approved by the U.S. Food and Drug Administration (FDA) for clinical use as well as regulated under compliance to HCT/P (Human Cell and Tissue Products) guidelines. However, various limitations and quality issues still plague most of the available DBM products, including many of the same disadvantages and practical shortcomings mentioned above in regard to allograft bone products.
One prime limitation with current systems relates to the alteration and degradation of physiologic structures, factors and components during conventional processing. During acid demineralization, most of the Osteogenic growth factors are removed and discard along with the acidic byproducts. The resulting collagen, mineral and protein microstructure is compromised and altered physiologically.
Another disadvantage of current DBM products is that they suffer from poor “wet field integrity,” i.e., their inability to remain intact when exposed to wet conditions. Thus, they tend to break up and/or fall apart in wet environments, such as is typically present in a surgical field, wherein blood, buffers, and other water-containing materials are present. Additionally, in such wet environments, current BM products tend to stick to surgeons' gloves while being reshaped and remodeled, creating a mess. Likewise, they tend to wash away partially while the surgical site is undergoing lavage. Another typical additive used by surgeons, i.e. Bone Marrow Aspirate (BMA), growth factors and/or cell preparations, which tend to alter handling deleteriously. To overcome these shortcomings, currently available BM products typically contain various additional materials to aid in holding the BM product together in the wet environment. Thus, binders and polymers are added, such as various poloxamers (nonionic triblock copolymers). It is highly desirable and advantageous, therefore, to provide DBM products that are 100% physiologic (i.e. no carrier) to better absorb growth factors and that exhibit wet field integrity, without the need for inclusion of binders, poloxamers, and the like.
Moreover, many currently available BM products even with addition of other factors are limited in their use by the need to add to them various carriers and delivery agents to facilitate their handling, injection, and implantation. Typical carriers include materials such as glycerin, carboxymethyl cellulose (commonly known as “CMC”), polymers (e.g. polaxomers) and the like. It is highly desirable and advantageous, therefore, to provide DBM products that are 100% physiologic, without the need to include carriers and delivery agents.
Additionally, many currently available BM products suffer from variability and inconsistency. This shortcoming arises from the fact that many DBM producers carry out their DBM production processes in multi-batch demineralization runs, followed by blending together the various batches.
Accordingly, there is an ongoing need to provide improved DBM products that overcome some or all of the disadvantages and shortcomings of existing DBM products. Likewise, there is an ongoing need to develop practical and economical methods for preparation of the improved DBM products.
Furthermore, there is a need to provide DBM products that are compliant with the standards of the American Association of Tissue Banks (AATB), i.e., having residual Ca+2 content <8%. Many current processes for generating DBM products tend to drastically or completely deplete the DBM of all minerals, including some important minerals that are known to possess osteogenic and osteoinductive properties.
The presently disclosed invention addresses these needs.